How can I populate a model with smaller models?
Take the Atlas figure, duplicate and apply a displace modifier that makes it smaller (just by a little bit). Use this to spawn particles from source: volume. This prevents any minifigs from sticking out through Atlas. This image shows roughly how the shape would change with a displace modifier. It would not be hollowed out like with a solidify modifier.

Create a particle system. Under render options choose render as object. Select the minifig as the object to render. Play around with particle scale and rotation until it looks good. Apply the particle system under modifiers. Now you have a whole bunch of minifigs filling Atlas.
Select all of the minifigs. Then Object&gt;Rigid Body&gt;Add Active. Now the minifigs will bounce off of each other and whatever objects you set as passive rigid bodies.
Under the material for the minifigs, add an object info node. Use the &quot;random&quot; input from this into a hue/saturation node in order to randomly alter the color of each individual minifig.